Conveying devices, such as those which are used for moving objects between different stations in a factory, usually comprise a conveying track in the form of a belt or a chain. The conveying tracks can be recessed in a trench with vertical side surfaces. Alternatively, they can be located on the horizontal upper surfaces of the trench or arranged in some other way. The objects to be conveyed are arranged slidably in relation to the conveying tracks, either directly or via supporting means. Larger objects are often conveyed on supporting means also known as pallets, and smaller objects may be conveyed using a small carrier often referred to as a carrier puck.
The conveyor chain is forwarded by a drive unit comprising a motor. The conveyor chains runs in conveyor beams and glides on slide rails attached to the conveyor beams. Both the conveyor chain and the slide rails may be made from a low friction material in order to reduce power consumption, to reduce wear and to reduce noise caused by vibrations. In the forward direction, i.e. when the chain transports objects, the underside of the upper body bears on upper slide rails of the conveyor beam. In the return direction, i.e. when the chain travels upside down in the return path, the upper side of the conveyor chain may be supported by a bearing surface on which the conveyor chain glides. The conveyor chain may also be provided with tabs or protrusions by which the chain may bear on an inner slide rail of the conveyor beam.
One problem with a sliding contact between the conveyor chain and the conveyor beams is that friction is created. The use of low friction materials in the chain links and in the slide rails reduces the friction. It is however not always possible to select a low friction material for the conveyor chain. Further, dust and other particles may set on the contact surfaces which lead to a higher friction and thus to a higher wear. Further, the sliding contact induces noise.
In U.S. Pat. No. 5,402,880 an article carrying chain is disclosed. The chain is to be used in an article conveyor and it includes a plurality of interconnected molded plastic chain link assemblies each having a planar top plate. A plurality of upper and lower tabs formed along the lower portions of the chain link assemblies serve to guide the chain relative to a pair of guide rails of the conveyor frame while permitting free removal of the chain link assemblies from the guide rails at selected areas along the length of the conveyor and also restraining the chain between the guide rails at other portions of the conveyor such as at curves or vertical bends.
U.S. Pat. No. 6,364,094 discloses a conveyor system comprising a conveyor chain, a chain guidance means and a guide support means. Each chain link comprise a link member, a connecting pin and a bearing element. The link members are provided with protrusions having through holes, adapted to hold the connection pin for the conveyor chain. Further, the conveyor chain will slide on the protrusions in the return path.
FR 2629804 and DE 101 51 863 describe further examples of similar conveyor chains.
These solutions work fine in some systems, but are anyhow subjected to the above mentioned problem. There is thus still room for improvements.